1. Field of the Invention
The present invention relates to a method of reducing a water-wave noise and a system thereof, and more particularly, to a method of reducing a water-wave noise and a system thereof capable of reducing water-wave noise for an analog to digital conversion by adjusting a sampling frequency and/or a noise frequency.
2. Description of the Prior Art
In a digital image system, an analog to digital converter (ADC) is utilized for converting an analog image signal into a digital format, in order to perform follow-up data processing and image displaying. Operations of the digital image system include performing sampling on an input analog image signal with a specific frequency, retrieving information related to image brightness and colors, and converting the information into the digital format to be outputted. The quality of the output images is influenced greatly during the sampling process due to the following two reasons: internal errors of the ADC generated from poor conversion linearity or clock offset, which may cause errors on sampling results; external noises generated from layout or configuration of system on a chip (SoC) or printed circuit board (PCB), where different methods of layout or configuration may exert influences of different magnitudes on the input signals of the ADC. Please refer to FIG. 1, which is a schematic diagram of an input signal of an ADC in an electronic system (e.g. a display) interfered with by an external noise. As shown in FIG. 1, after the analog input signal is interfered with by the external noise, the noise is combined with the original input signal and then sampled by the ADC, which may cause the quality of the output image to be damaged. In the SoC, the signals closest to the ADC (especially the clock signals) may interfere with the analog input signal of the ADC more easily.
Among the second type of noise/interference, one particular type of noise is called a water-wave noise. The water-wave noise is generated by a signal sampled by the ADC having periodic noise and transmitted to a display, such that ripples appear on the display continuously moving in the same direction like ripples on the surface of a lake; hence the name “water wave”. Waveforms of the water-wave noise generated by the interfered analog input signal sampled by the ADC are illustrated in FIG. 2. As shown in FIG. 2, a periodic noise can be considered as a clock. A smooth analog input signal is interfered with by the periodic noise, and then sampled by the ADC with a specific sampling frequency. This generates the water-wave noise.
There have been many documents discussing the first type of noise/interference, with related solutions for enhancing the performance of the ADC. When the second type of noise/interference and especially the water-wave noise is encountered, however, the interference is usually prevented by modifying the layouts or configurations to isolate the source of noise as much as possible. Another solution comprises a method similar to time division multiplexing (TDM), which separates the time of transmitting the input signal and the time of transmitting the interference signal. These two solutions, however, may violate system requirements and always cause poor performance; especially in recent years, as systems are interfered with by noise more severely due to miniaturization of electronic products and processes. Therefore, there is a need to provide a method for preventing the quality of output images from being damaged by the water-wave noise.